1. The Field of the Invention
The invention relates to a radio transmission system using the generalized frequency divisional multiplexing (GFDM) method. In particular the invention relates to applying a Walsh-Hadamard transformation to a block of GFDM data symbols.
2. The Relevant Technology
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. The use of the term “background” is inclusive of the term “context.” Thus, the following section provides both context for the disclosure and may also provide patentable support for the claims.
The so-called GFDM system is a recent physical layer (PHY) scheme proposed to address the challenges for 5th generation cellular systems with opportunistic use of frequency spectrum and relaxed synchronization. The GFDM system provides a fast, flexible scalable and content aware physical layer scheme which at the same time is robust and reliable, while using vacant frequency bands, e.g. so-called TV white spaces. The basic GFDM system has been described in “GFDM—Generalized Frequency Division Multiplexing” by Fettweis et al., IEEE VTC spring 2009.
Though the GFDM system shares some properties with well-known OFDM systems, there are significant differences. While both systems may divide an available frequency band into at least two adjoining sub-bands, the GFDM system may deploy individual transmission parameters for each of the at least two sub-bands while in OFDM the transmission parameters deployed in the sub-bands are similar or identical, i.e. uniform.
In contrast thereto the Generalized Frequency Division Multiplexing, GFDM, is a multicarrier scheme that uses pulse-shaping per subcarrier to achieve low out-of-band emissions OOBE, i.e. low out-of-band interference. Typically a prototype filter is used to pulse-shape a number of K subcarriers, wherein the filter impulse response is circularly shifted by K samples to obtain the pulse-shape for each time slot. This technique is known as tail-biting and eliminates the filtering tails, thus allowing a block-based data structure, where a number of M·K data symbols are transmitted using a number of K subcarriers, each subcarrier carrying a number of M data symbols per block.
The GFDM can be properly parameterized to address scenarios currently foreseen for the fifth generation of mobile communications, i.e. 5G. Single shot transmissions as required for the so-called tactile internet and random channel access as well as machine-to-machine communications and other low latency applications are challenging scenarios. In particular low-latency requirements prevent the use of retransmission protocols. Instead the data shall be reliably transmitted from source to sink using a single transmission burst, i.e. no retransmission, which at the same time avoids the use of long channel codes or interleavers. However, at least one drawback of using short single-shot transmission using GFDM occurs in frequency selective channels. Deep notches in the frequency response of a channel may lead to unrecoverable burst errors at the receiver side.